Many individuals require partial immobilization, to protect a traumatized joint. Ideally, this partial immobilization would allow the joint to move through a predetermined range of motion that is necessary for limited locomotion and healing, but not through a range of motion that is injurious to the joint or painful to the individual. Further, it would also be ideal to be able to increase mobility in a controlled manner as the joint begins to heal.
Referring to FIG. 1 it can be seen that the hip joint is a ball-and-socket joint formed by the joining of the head of the femur 60 into the cup-shaped cavity of the pelvic bone, referred to as the acetabulum 62. Being a ball-and-socket joint the movements of the hip are extensive, consisting of three axes of rotation--flexion-extension (the bending motion of the hip joint), internal and external rotation (rotation of the lower limb about its longitudinal axis) and abduction-adduction (the lateral motion of the hip joint). The normal active ranges of motion for the hip joint are approximately: hip flexion 121.degree., hip extension 19.degree., hip abduction 43.degree., hip internal rotation 45.degree., and hip external rotation 45.degree.. Roach, K. E. and Miles, T. P., "Normal Hip and Knee Active Range of Motion: The Relationship to Age", Physical Therapy, 1991, 71:9, 656-665.
Because the neck of the femur 64 is a long segment of bone which joins the shaft 66 at an abrupt angle all movements of the thigh result from movements of the head and neck segment rather than the shaft of the femur. As an example, flexion and extension of the thigh are caused by rotation of the head and neck segment of the femur along an axis as shown in FIG. 1. Furthermore, the head and neck segment rotate outward as the leg flexes forward. During abduction and adduction of the thigh, the head and neck segment move within the plane established by their angle, and result from a bending in the joint with some rotation caused by the normally forward inclination of the neck of the femur. In other words, rather than merely bending about a pivot axis, the normal motion of the hip joint includes pivoting at an axis that slides in relation to the joint to produce a "component motion" in more than one plane.
Numerous devices have been developed for immobilizing the hip joint. Illustrative of traditional prior art devices is U.S. Pat. No. 4,481,941 by Rolfes, which accommodates the flexion-extension or bending motion of the leg while preventing any lateral or rotational movement. Thus, a major drawback of traditional devices is that they do not mimic the ball-and-socket movement of hip joint in that they pivot at a single fixed axis and move through a single plane. Typical of more recent prior art devices is U.S. Pat. No. 4,881,532 by Borig, et al. The more recent devices are designed to provide for two axes of motion--flexion-extension and abduction-adduction. The Borig device, for example, is comprised of an upper and lower control arm which contains two hinges. One hinge provides for a range of rotation of the hip brace during flexion and extension of the hip and the second hinge provides for a range of rotation of the brace during abduction and adduction of the hip. The Borig device can be adjusted for free abduction motion up to 30.degree..
It is readily apparent that none of the prior art devices make any attempt to account for the rotation of the lower limb about its longitudinal axis as the leg flexes forward or laterally. Accordingly, there is a need for an orthopedic hinge for use with hip joint braces that provides for free external and internal rotation of the hip joint within a controlled range.